Description

RPC library routines allow C language programs to make procedure calls
on other machines across the network. First, the client calls a procedure
to send a request to the server. Upon receipt of the request,
the server calls a dispatch routine to perform the requested service and then
sends back a reply.

The clnt_call(), rpc_call(), and rpc_broadcast() routines handle the client side of the
procedure call. The remaining routines deal with error handling.

Some of the routines take a CLIENT handle as one of the
parameters. A CLIENT handle can be created by an RPC creation
routine such as clnt_create(). See rpc_clnt_create(3NSL).

These routines are safe for use in multithreaded applications. CLIENT handles can
be shared between threads; however, in this implementation requests by different threads
are serialized. In other words, the first request will receive its results
before the second request is sent.

Routines

A function macro that calls the remote procedure procnum associated with the client handle, clnt, which is obtained with an RPC client creation routine such as clnt_create(). See rpc_clnt_create(3NSL). The parameter inproc is the XDR function used to encode the procedure's parameters, and outproc is the XDR function used to decode the procedure's results. in is the address of the procedure's argument(s), and out is the address of where to place the result(s). tout is the time allowed for results to be returned, which is overridden by a time-out set explicitly through clnt_control(). See rpc_clnt_create(3NSL).

If the remote call succeeds, the status returned is RPC_SUCCESS. Otherwise, an appropriate status is returned.

clnt_send()

Use the clnt_send() function to call a remote asynchronous function.

The clnt_send() function calls the remote function procnum() associated with the client handle, clnt, which is obtained with an RPC client creation routine such as clnt_create(). See rpc_clnt_create(3NSL). The parameter proc is the XDR function used to encode the procedure's parameters. The parameter in is the address of the procedure's argument(s).

By default, the blocking I/O mode is used. See the clnt_control(3NSL) man page for more information on I/O modes.

The clnt_send() function does not check if the program version number supplied to clnt_create() is registered with the rpcbind service. Use clnt_create_vers() instead of clnt_create() to check on incorrect version number registration. clnt_create_vers() will return a valid handle to the client only if a version within the range supplied to clnt_create_vers() is supported by the server.

RPC_SUCCESS is returned when a request is successfully delivered to the transport layer. This does not mean that the request was received. If an error is returned, use the clnt_getterr() routine to find the failure status or the clnt_perrno() routine to translate the failure status into error messages.

clnt_freeres()

A function macro that frees any data allocated by the RPC/XDR system when it decoded the results of an RPC call. The parameter out is the address of the results, and outproc is the XDR routine describing the results. This routine returns 1 if the results were successfully freed; otherwise it returns 0.

clnt_geterr()

A function macro that copies the error structure out of the client handle to the structure at address errp.

clnt_perrno()

Prints a message to standard error corresponding to the condition indicated by stat. A newline is appended. It is normally used after a procedure call fails for a routine for which a client handle is not needed, for instance rpc_call()

clnt_perror()

Prints a message to the standard error indicating why an RPC call failed; clnt is the handle used to do the call. The message is prepended with string s and a colon. A newline is appended. This routine is normally used after a remote procedure call fails for a routine that requires a client handle, for instance clnt_call().

clnt_sperrno()

Takes the same arguments as clnt_perrno(), but instead of sending a message to the standard error indicating why an RPC call failed, returns a pointer to a string that contains the message.

clnt_sperrno() is normally used instead of clnt_perrno() when the program does not have a standard error, as a program running as a server quite likely does not. clnt_sperrno() is also used if the programmer does not want the message to be output with printf(), or if a message format different than that supported by clnt_perrno() is to be used. See printf(3C). Unlike clnt_sperror() and clnt_spcreaterror(), clnt_sperrno() does not return a pointer to static data. Therefore, the result is not overwritten on each call. See rpc_clnt_create(3NSL).

clnt_sperror()

Similar to clnt_perror(), except that like clnt_sperrno(), it returns a string instead of printing to standard error. However, clnt_sperror() does not append a newline at the end of the message.

clnt_sperror() returns a pointer to a buffer that is overwritten on each call. In multithreaded applications, this buffer is implemented as thread-specific data.

rpc_broadcast()

Similar to rpc_call(), except that the call message is broadcast to all the connectionless transports specified by nettype. If nettype is NULL, it defaults to netpath. Each time it receives a response, this routine calls eachresult(), whose form is:

where out is the same as out passed to rpc_broadcast(), except that the remote procedure's output is decoded there. addr points to the address of the machine that sent the results, and netconf is the netconfig structure of the transport on which the remote server responded. If eachresult() returns 0, rpc_broadcast() waits for more replies; otherwise, it returns with appropriate status.

The broadcast file descriptors are limited in size to the maximum transfer size of that transport. For Ethernet, this value is 1500 bytes. rpc_broadcast() uses AUTH_SYS credentials by default. See rpc_clnt_auth(3NSL).

rpc_broadcast_exp()

Similar to rpc_broadcast(), except that the initial timeout, inittime and the maximum timeout, waittime, are specified in milliseconds.

inittime is the initial time that rpc_broadcast_exp() waits before resending the request. After the first resend, the retransmission interval increases exponentially until it exceeds waittime.

rpc_call()

Calls the remote procedure associated with prognum, versnum, and procnum on the machine, host. The parameter inproc is used to encode the procedure's parameters, and outproc is used to decode the procedure's results. in is the address of the procedure's argument(s), and out is the address of where to place the result(s). nettype can be any of the values listed on rpc(3NSL). This routine returns RPC_SUCCESS if it succeeds, or it returns an appropriate status. Use the clnt_perrno() routine to translate failure status into error messages.

The rpc_call() function uses the first available transport belonging to the class nettype on which it can create a connection. You do not have control of timeouts or authentication using this routine.